What is epoxy coated rebar and why is it being banned?

in this video I'm gonna talk about it poxy could have reinforcing steel and why many people are moving away from it well talk about other technologies that can be used for long corrosion inside your reinforced concrete and at the end I will talk about my favorite technology the one that I think is the best but you got to wait till the end for that one my name is Tyler Leigh and I got a secret I've kind of got a crush on concrete corrosion of rebar inside concrete is a huge deal many people say that it is the most costly the most damaging and the most scary of the durability mechanisms for concrete so how does this happen well one method is that chlorides come from the outside of the concrete and they come in over time and more and more and finally when they get to the reinforcing steel they break something down called the passive layer and it starts corrosion now the corrosion doesn't happen in one spot the passive layer goes away everywhere and the corrosion happens pretty much uniformly around the bar so corrosion begins when the chlorides reach this critical level at the bar this is called the chloride threshold level and I've talked more about it in previous videos a common way to deal with corrosion of metals is to paint them I've shown a picture of the Golden Gate Bridge here did you know that they start on one side of the Golden Gate Bridge and continuously paint it from one side to the other and once they finish they start over again and paint it again because they're so scared of corrosion and here's a picture from the top what if this is your job this guy's done painting and he knows in about a year he's gonna be back at the exact same spot well why don't we do this for the rebar that goes inside concrete guess what we can here's a picture of that process here a rebar that's being powder-coated with this epoxy type material or like a paint on the surface of the bar itself now this is commonly used you can see this on a bridge deck and if you've ever seen green rebar then ladies and gentlemen you have seen the infamous epoxy coated reinforcing bar now it's pretty cool it's pretty widely used there's lots of people that that that use it because they're concerned about corrosion and they want to apply it on the surface of the rebar and their thought is that it's going to help keep the outside chlorides from getting to the rebar and reaching this this chloride threshold level is starting some type of corrosion but research done on field structures by Texas Florida Virginia and Ontario d-o-t so those do T's in America and in Canada have found poor performance of epoxy coated reinforcing bar in the field now Virginia is the most quoted of these they looked at 18 different bridges and they found that after four years that 90% of the epoxy-coated rebar was d bonded what why does this happen want to learn more let's look at a rebar now if you just look over it you look really really careful you'll see right around here there's kind of a spot let's zoom in we get closer again we see that spot let's zoom in even further I knew that was damaged that's where in handling the bar this spot has been rubbed off the epoxy has been removed and it's not just in one spot as we're getting closer there's certain spots that our eyes couldn't even see you can see them here and here and you see these Nick's right here that's our small scratches inside the epoxy coating that's scratchy to go all the way through nobody really knows now it kind of makes sense that rebar is kind of handled heavily excessively they're kind of mean to it they kind of beat on it and drag it and bend it and tie it and cut it and do all kinds of things to it so it makes sense that in this coating there might be some Nicks so what are the issues with this well there's two big ones let's talk about the first one well if you have a damaged spot well the chlorides come in and get closer and they get closer and they start corrosion well corrosion doesn't happen uniformly over the bar corrosion is gonna happen in one spot all of that corrosion instead of happening at the surface is gonna be concentrated in one region and this is called pitting corrosion this is this accelerated corrosion one region and this is scary this can cause your bars to break suddenly in one location where these holidays or these damaged regions are here's a picture of this accelerated corrosion from bars that are being exposed you can see this bar is corroding kind of uniformly throughout but this part and that one spot has this deep pitting corrosion so what's another issue that can happen I said there was - the other thing that can happen is at the surface there's actually starts to be deep bonding the chlorides work their way up and start to pull up the actual rebar some of that may be corrosive products some of it may be something else but it may just be a chemical change of the epoxy nobody really knows and over time it deep bonds and then it D bonds more and there's just this pocket underneath the bar and this is what Virginia saw this deep bonding of the reinforcing what this looks like is you'll see a discoloration in the epoxy coating and that means it's not really bonded or along the length so what what can you do about this well you can do special tie wires okay you can be very very careful how you handle the bars you can see even on this one they try to take all these special care and look I see a nick right there what you're supposed to do is get out with this special paint and coat that spot do you think you're gonna catch every spot in a bridge or in a building are you gonna miss any well if you do those are weak spots where corrosion may happen but are there other solutions to this oh baby there's tons of them there's all kinds of people working on this all kinds of companies trying to make this happen some people are trying to do improve coatings around the rebar others are trying to change the rebar all together use different chemical types use stainless rebar use this Chrome modify this poor man's poor man's stainless rebar use fiber reinforced plastic she's basalts or glass there's all kinds of different solutions out there but why aren't these more popular well number one they'll cost poor because they're not really widely produced and civil engineering is totally awesome one thing about it is that we deal in high volumes so our costs have to be low I like to say we're like the Walmart or the Amazon of engineering we're dealing huge volumes of stuff so we need to make it cheap we try to make things more expensive it doesn't work really well in our systems availability is another issue even if we wanted to make every single rebar stainless steel we couldn't we don't produce enough every year all these rebars to are not addressed in our building codes right now the only thing that is addressed is normal rebar and epoxy coated so structural engineers and they're trying to decide how these three bars are gonna change things I don't know what to do because the codes don't give them guidance ah but there's some great research coming out I'm gonna reference it in the notes below and I think this is gonna change I think there's gonna be more guidance in the future but what do I think's best I know if I didn't answer this question I would get it in my comments below I think personally that galvanized rebar is the best solution why because it's a balanced number one it increases your chloride threshold level by 2 to 4 times number 2 the cost increase is minimal it's less than 10% of the cost of the rebar and it's widely available hot dip galvanizing taking rebar and dipping it in molten zinc and taking it out that's a widely used process used in all types of metal treatment there's proven fill performance with it and there's minimal impact on your structural design and that's why for me I think it's the best choice now it may not be for you and if it's not I want you to tell me why in the comments below also you got to watch out for hot dip galvanizing when you put it in the fresh cement paste some of the galvanizing will be eaten away but there's a solution to this you just use a thicker layer of galvanizing if you liked this video please give me a thumbs up subscribe to my channel leave me a comment take care bye [Music] [Music]

Channel: Tyler Ley

Views: 490,375

Rating: 4.712429 out of 5

Keywords: #simple concrete, #concrete durability, reinforcing steel, rebar, passive layer, epoxy coated rebar, concrete, tyler ley, service life, corrosion, concrete corrosion, rebar corrosion, concrete service life, galvanized rebar, mmfx, stainless rebar, basalt rebar, FRP rebar, concrete structure, structural engineering, durability, rebar epoxy coating

Id: xVDy84rR5Z8

Length: 9min 47sec (587 seconds)

Published: Fri Sep 28 2018